1. Field of the Invention
This invention relates to a condensing apparatus for use in a refrigeration cycle applied to an air-conditioning system for automobiles, buildings, etc., and also relates to a receiver-dryer used for such a condensing apparatus.
2. Description of Related Art
FIG. 6 shows an expansion-valve system refrigeration cycle as one of typical refrigeration cycles. In the refrigeration cycle, the gaseous refrigerant of high temperature and high pressure sent out from a compressor CP is introduced into a condenser CD and exchanges heat with the ambient air to be cooled and condensed therein. The condensed refrigerant mostly in a liquefied state flows into a receiver-tank RT to be separated into a gaseous refrigerant and a liquefied refrigerant. Then, only the liquefied refrigerant flows out of the receiver-tank RT. The liquefied refrigerant is decompressed and expanded by an expansion-valve EV, and is introduced into an evaporator EP as a mist-like refrigerant of low pressure and low temperature. This mist-like refrigerant evaporates in the evaporator EP by absorbing latent heat from the ambient air to be turned into a gaseous refrigerant. Then, the gaseous refrigerant flows out of the evaporator EP, and is inhaled by the compressor CP. In FIG. 6, the spotted area indicates that a refrigerant is in a liquid state. In the meantime, the refrigeration flow rate is controlled by adjusting the opening degree of the expansion-valve EV in response to the signal sent from the heat-sensitive-coupler SC provided at the outlet side of the evaporator EP.
By the way, when the subcooling degree of the refrigerant condensed in the condenser CD is insufficient, the condensed refrigerant is unstable such that the refrigerant evaporates when it receives small quantity of heat and/or a small pressure loss occurs at a downstream side. This often causes deterioration and/or fluctuation of the refrigeration cycle efficiency. To cope with the above-mentioned problems, conventionally, a subcooling portion, which subcools the refrigerant condensed by the condenser CD to a temperature lower than the condensation temperature of the refrigerant by about 2-5.degree. C., is provided so as to send the condensed refrigerant to the evaporator side as a stabilized liquid refrigerant. Usually, this subcooling portion is arranged at the downstream side of the receiver-tank RT. In many cases, such a subcooling portion is integrally provided to the condenser CD in view of the space efficiency.
On the other hand, in many cases, a receiver-dryer is used as the aforementioned receiver-tank RT. The receiver-dryer is provided with a desiccant-filled-portion therein to absorb the moisture components of the refrigerant. Such a receiver-dryer includes the so-called sandwich-type receiver-dryer having an upper space 33 above a desiccant-filled portion 32 and a lower space 34 below the desiccant-filled portion 32 as shown in FIGS. 8A-8C and the so-called bag-type receiver-dryer provided with a desiccant-filled portion 32 in one side therein as shown in FIG. 8D.
In the receiver-dryer having a sucking-pipe 36 shown in FIG. 8A, the refrigerant flowed into the upper space 33 via the refrigerant inlet 35 passes through the desiccant-filled-portion 32 to reach the lower space 34. Then, the liquefied refrigerant separated from the gaseous refrigerant is sucked up by the sucking-pipe 36 and flows out from the refrigerant outlet 37 provided at the top of the tank.
In the receiver-dryer having a supplying-pipe 38 shown in FIG. 8B, the refrigerant introduced from the refrigerant inlet 35 provided at the bottom portion flows up the supplying-pipe 38 to reach the upper space 33, and then passes through the desiccant-filled-portion 32 to reach the lower space 34. Then, the liquefied refrigerant separated from the gaseous refrigerant flows out from the refrigerant outlet 37 provided at the bottom of the tank.
In the inlet-outlet-confrontation-type receiver-dryer shown in FIG. 8C, the refrigerant introduced into the upper space 33 via the top refrigerant inlet 35 passes through the desiccant-filled-portion 32 to reach the lower space 34. Then, the liquefied refrigerant separated from the gaseous refrigerant flows out from the refrigerant outlet 37 provided at the bottom of the tank.
In the bag-type receiver-dryer shown in FIG. 8D, the refrigerant flowed into the tank via the refrigerant inlet 35 provided at the side portion of the tank contacts the desiccant-filed-portion 32, and the liquefied refrigerant separated from the gaseous refrigerant in the lower portion of the tank flows out from the refrigerant outlet 37 provided at the bottom of the tank. Among this bag-type receiver-dryer, there are a receiver-dryer having an outlet and an inlet both provided at an upper portion or a lower portion of a tank and a receiver-dryer having an outlet and an inlet provided at an upper portion and a lower portion of a tank, respectively.
In an air-conditioning system, it is always desired to improve the space efficiency and performance. Especially, in an automobile air-conditioner, in order to effectively use the limited body space, it is requested that the whole system be further miniaturized. In order to realize the aforementioned requests, it is necessary to reduce the amount of refrigerant sealed in the refrigeration cycle, to enhance the performance stability to load fluctuation (overcharge toughness) and to prevent performance deterioration with time due to continuous running (decline of leakage toughness). For this purpose, it is desired to secure a steady region, i.e., a stable region in a subcooled state of the refrigerant to the amount of sealed refrigerant, as widely as possible.
FIG. 7 is a correlation characteristic figure showing the correlation between a subcooling degree of the condensed refrigerant and an amount of sealed refrigerant obtained by a charge examination (cycle bench) of an automobile air-conditioner. In this correlation characteristic figure, it is ideal that the rising curve is steep until it reaches a steady region as shown by the phantom-line curve B and that the steady region has a wider range. However, in an automobile air-conditioner using a conventional subcooling system condenser, the rising curve is gentle until it reaches the steady region as shown by the solid-line curve A. Therefore, the steady region starting point delays toward the larger amount of a sealed refrigerant side, which results in a delayed refrigerant sealing timing and a narrow steady region width. This means that in the conventional automobile air-conditioner the miniaturization by decreasing the sealed refrigerant amount is difficult, the performance stability to load fluctuation is bad, and the performance tends to deteriorate with time due to continuous running.
The inventors investigated causes of the above-mentioned problems of the conventional automobile air-conditioner from various aspects so as to realize a miniaturized high-performance automobile air-conditioner. Consequently, the inventors revealed that one factor of the above-mentioned problems resides in a structure of a conventional receiver-dryer RD. That is, since the interface between the liquefied refrigerant and the gaseous refrigerant, i.e., the surface of the liquefied refrigerant, near the refrigerant outlet of the receiver-dryer RD is hard to become stable, the stable supply of the liquefied refrigerant to the following cycle part cannot be performed. Furthermore, a large amount of gaseous refrigerant will be mixed into the liquefied refrigerant to be flowed out. Therefore, the above-mentioned steady region becomes narrower and the steady region starting point delays toward the larger amount of a sealed refrigerant side.
That is, since a refrigerant flow velocity flowing into a receiver-dryer RD from a condenser CD is generally high, in a sandwich-type receiver-dryer, larger turbulence of the liquefied refrigerant occurs in the upper space 33 into which the refrigerant is introduced. Consequently, since the liquefied refrigerant stagnates in the upper space 33, the liquefied refrigerant is not fully supplied to the lower space 34. As a result, a few amount of liquefied refrigerant accumulated in the lower space 34 is disturbed by the high-speed liquid flow passed through the desiccant-filled-portion 32, which causes bubbles of gaseous refrigerant. For this reason, it is assumed that a gaseous refrigerant flows out of the refrigerant outlet 37 exposed to the gaseous phase due to large surface fluctuation, and/or a lot of air bubbles are involved into the liquefied refrigerant to be flowed out.
On the other hand, in the bag-type receiver-dryer, it is assumed that since the internal refrigerant flow velocity and the turbulence of the internal refrigerant are larger than in the sandwich-type receiver-dryer, the liquefied refrigerant surface near the refrigerant outlet 37 becomes further unstable, resulting in a larger outflow of gaseous refrigerant.
Accordingly, the inventors further conducted the researches based on the above-mentioned knowledge, and found out the followings and completed the present invention. That is, an adoption of a specific structure of a receiver-dryer stabilizes a surface of a liquefied refrigerant separated from a gaseous refrigerant near a refrigerant outlet, which enables a stable supply of the liquefied refrigerant to the following cycle part. In addition, bubbles of a gaseous refrigerant smoothly change to a gaseous refrigerant at the interface of the gaseous refrigerant and the liquefied refrigerant, and the mixing of the gaseous refrigerant into the liquefied refrigerant to be flowed out is decreased effectively. This enables a decreased amount of sealed refrigerant of a refrigeration cycle, and an enlarged steady region of the refrigerant to the amount of sealed refrigerant making the best use of the capacity of the receiver-dryer. Consequently, it is possible to provide a condensing apparatus suitably used for an automobile air-conditioner using a subcooling system condenser.